1. Field of the Invention
The present invention relates to computer graphics technology. More specially, the present invention relates to the design of a graphics pipeline.
2. Related Art
Computer systems are extensively used to perform a wide variety of useful operations in modern society. Applications of computer systems can be found in virtually all fields and disciplines, including but not limited to business, industry, scientific research, education and entertainment. For instance, computer systems are used to analyze financial data, to control industrial machinery, to model chemical molecules, to deliver classroom presentations and to generate special effects for movies. Indeed, it has now come to the point where many of these operations have become so computationally intensive that they cannot be efficiently performed without the help of modern computer systems. As part of the process of performing such operations, computer systems typically utilize some type of display device, such as a cathode ray tube (CRT), a liquid crystal display (LCD) and the like, in order to display images and data which are recognizable to their users. As such, computer systems typically incorporate functionality for generating images and data which are subsequently output to the display device.
One technique for generating computer images and viewable data within a computer system is to utilize a graphics pipeline, which uses a series of interconnected functional blocks of circuitry, or “stages”, to render an image. Each stage performs a unique task during each clock cycle. As soon as one stage has completed its task on a pixel, that stage can immediately proceed to work on the next pixel. It does not have to wait for the processing of a prior pixel to complete before it can begin processing the current pixel. More specifically, sets of graphics primitives are specified within the computer system and are subsequently sent down the graphics pipeline. Each stage sequentially performs a different function or functions on the received graphics primitives and then passes that data onto the following stage. Eventually, the graphics pipeline manipulates the graphics primitives in order to produce the final pixel values of an image. Thus, a graphics pipeline enables different graphics data to be processed concurrently, thereby generating graphics images at a higher rate. It should be appreciated that the functionality of a typical prior art graphics pipeline is well known by those of ordinary skill in the art.
However, a typical prior art graphics pipeline does not operate efficiently. More specifically, the memory system used with a typical graphics pipeline inherently has a high memory latency and a high bandwidth. Such a memory system performs optimally when data is bursted in and out of the memory system. Due to this inherent high memory latency, the graphics pipeline often has to wait a long time for requested data to arrive after issuing a memory request. On the other hand, processing in the graphics pipeline cannot proceed until the data is received. As such, the high memory latency adversely impacts the throughput of the graphics pipeline and thus lowers the overall performance of the computer system. As the complexity of graphics applications continue to increase, the performance of computer systems using these prior art graphics pipelines will become even more severely impacted.
Another problem with a typical prior art graphics pipeline is that it uses span traversal during rasterization which causes much unused data to be retrieved, thus resulting in more inefficiency. More particularly, the rasterizer of a typical graphics pipeline traverses the graphics primitives in a span fashion. Unfortunately, span traversal in two-dimensional (2-D) graphics rendering usually results in retrieving a large amount of data that does not end up being used by the pipeline operations. This means that much computing resource is wasted in performing operations that are not useful. Such wasteful use of resource adversely impacts the throughput of the graphics pipeline and thus lowers the overall performance of the computer system.
Thus, there exists a need for a graphics pipeline which does not operate inefficiently due to the high memory latency of the memory system and which does not waste computing resource on operations that are unproductive.